1. Field of the Invention
The present invention relates to a vinyl chloride resin composition useful for molded articles of the crosslinked vinyl chloride series of resins, which can be easily processed by common plastics processing machinery. The molded articles possess smooth surfaces and are excellent in appearance. Furthermore, they possess improved physicl properties such as permanent strain and recovery properties under compression and high-temperature deformation characteristics.
2. Description of the Prior Art
Vinyl chloride resin (hereinafter abbreviated as "PVC") is widely utilized in various fields of application because its hardness can be easily controlled by changing the amount of plasticizer blended with the resin. Also, the resin can be processed at high speed by common plastics processing machinery and is characterized by excellent weatherability and non-flammability. However, on the other hand, PVC resins have the disadvantage that under compression the permanent strain induced is substantial and the recovery chracteristics are poor. Furthermore, the resins easily deform at elevated temperatures. Various methods of crosslinking, PVC during processing have been attempted to improve these deficiencies. For example, the resin has been cross-linked through the mechanism of an ionic reaction as represented by a method in which magnesium oxide, zinc oxide or the like is blended with the resin. However, this technique is of no practical value since it promotes the decomposition of PVC through reaction of the chlorine atom in PVC. Another technique is known in which PVC is crosslinked during processing by a reaction between functional groups introduced into the molecule or by the ionic reaction of a functional group with a crosslinking agent. However, this method cannot be generally used as a manufacturing method for molded articles of crosslinked PVC because it is deficient from the point of view that crosslinking takes place during kneading in the processing step which makes molding impossible because of the narrow temperature processing range of PVC series resins or because the molded articles are substantially colored as a result of being crosslinked upon heating above the decomposition temperature of PVC. Another method of crosslinking is a radical polymerization reaction with a peroxide. This method is difficult as a general method since crosslinking tends to easily take place during kneading and, in addition, the molded article produced is substantially colored because the radical decomposition of PVC is promoted.
For the reasons presented above it can be readily appreciated that it is difficult to mold and cross-link PVC by common processing machinery in the manufacture of molded articles of cross-linked PVC, since PVC which is easily decomposed by heat, requires high processing temperatures and processes a very narrow processing temperature range.
A need continues to exist for a method of improving the characteristics of PVC resin so that the same is more amenable to processing to form molded articles therefrom.